Anticoagulant Rodenticide Exposure in Birds of Prey in Massachusetts

Anticoagulant rodenticides are used to control rodent populations in various settings, including urban, suburban and agricultural areas. These rodenticides disrupt blood clotting pathways, resulting in excessive bleeding and death. While effective in controlling rodent overpopulation, these poisons can also cause mortality in non-target species of mammals and birds that ingest the bait (primary exposure) or ingest poisoned animals (secondary exposure).

Brodifacoum is a second-generation anticoagulant rodenticide that is currently available for household use in a variety of forms, including bait blocks and pellets. This compound presents a high risk for unintended poisoning of wildlife due its long persistence time in liver tissue. Brodifacoum is the rodenticide that has been identified in birds of prey suffering from anticoagulant rodenticide toxicosis that have been treated at Tufts Wildlife Clinic.

The most frequent species treated at Tufts Wildlife Clinic for anticoagulant rodenticide toxicosis is the red-tailed hawk (Buteo jamaicensis), which predominantly feeds on small- to medium-sized mammals but will also consume birds. Affected hawks present extremely anemic and weak with evidence of profuse bleeding from minor lacerations or extensive bruising with no evidence of serious traumatic injuries such as fractures. If these birds are not found and treated they will die due to blood loss. However, if they are found in time and receive aggressive medical treatment for blood loss and the antidote for the rodenticide (vitamin K-1), they can recover and be released back to the wild.

The clinical cases treated at Tufts Wildlife Clinic, together with reports on widespread anticoagulant rodenticide exposure in birds of prey in New York state, led to an ongoing project intended to survey the extent of exposure of birds of prey in urban and suburban areas of Massachusetts to these compounds. Species included in this study are red-tailed hawks, barred owls (Strix varia), eastern screech owls (Otus asio), and great horned owls (Bubo virginianus).

Documenting the presence of these rodenticides in predators such as birds of prey reflects the far-reaching effects of human activity on environmental health. As rodent populations flourish in human-altered landscapes, attempts to control these populations have potential consequences for animals higher in the food chain. This project, therefore, demonstrates a fundamental concept of conservation medicine: the interconnectedness of humans, animals and ecosystems.